<template>
	<view class="u-wrap">
		<view class="u-menu-wrap">
			<scroll-view scroll-y scroll-with-animation class="u-tab-view menu-scroll-view" :scroll-top="scrollTop"
				:scroll-into-view="itemId">
				<view v-for="(item,index) in tabbar" :key="index" class="u-tab-item"
					:class="[current == index ? 'u-tab-item-active' : '']" @tap.stop="swichMenu(index)">
					<text class="u-line-1">{{item.name}}</text>
				</view>
			</scroll-view>
			<scroll-view :scroll-top="scrollRightTop" scroll-y scroll-with-animation class="right-box"
				@scroll="rightScroll">
				<view class="page-view">
					<view class="class-item" :id="'item' + index" v-for="(item , index) in tabbar" :key="index">
						<view class="item-title">
							<text>{{item.name}}</text>
						</view>
						<view class="item-container">
							<view class="thumb-box" v-for="(item1, index1) in item.foods" :key="index1">
								<image v-if="item1.icon != ''" class="item-menu-image" :src="item1.icon" mode="">
								</image>
								<view v-else class="item-menu-image row-c" style="background-color: #F4F6F8;"><text
										style="font-size: 20rpx;color: #d0d0d0;">加载失败</text></view>
								<view class="item-menu-name">{{item1.name}}</view>
							</view>
						</view>
					</view>
				</view>
			</scroll-view>
		</view>
	</view>
</template>


<script>
	export default {
		data() {
			return {
				scrollTop: 0, //tab标题的滚动条位置
				oldScrollTop: 0, // tab标题的滚动条旧位置
				current: 0, // 预设当前项的值
				menuHeight: 0, // 左边菜单的高度
				menuItemHeight: 0, // 左边菜单item的高度
				itemId: '', // 栏目右边scroll-view用于滚动的id
				tabbar: [{
						"name": "蔬菜水果",
						"foods": [{
								"cat": 383,
								"name": "蔬菜",
								"icon": "http://nq348.com/uploads/category/20220315/1aeed6fa43b54cd68cce0c4883160f91.png",
								"key": "蔬菜"
							},
							{
								"cat": 384,
								"name": "食用菌",
								"icon": "http://nq348.com/uploads/category/20220418/09839c618b35b510d50151f9a17793ee.png",
								"key": "食用菌"
							},
							{
								"cat": 385,
								"name": "水果",
								"icon": "http://nq348.com/uploads/category/20220418/5294ad2fc7effc9629cbfdb8baf41773.png",
								"key": "水果"
							}
						]
					},
					{
						"name": "畜禽养殖",
						"foods": [{
								"cat": 388,
								"name": "禽类",
								"icon": "http://nq348.com/uploads/category/20220418/da31895fc5a9aacf93fea6f27f08afd7.png",
								"key": "禽类"
							},
							{
								"cat": 389,
								"name": "畜类",
								"icon": "http://nq348.com/uploads/category/20220418/6352081e3f3b36f9360a933676e9452c.png",
								"key": "畜类"
							},
							{
								"cat": 391,
								"name": "蛋类",
								"icon": "http://nq348.com/uploads/category/20220418/d2e7ab4224679c0c796ba3ddd8a68e2f.png",
								"key": "蛋类"
							},
							{
								"cat": 390,
								"name": "水产",
								"icon": "http://nq348.com/uploads/category/20220418/52a1f1baa7617ef4d4e1a4b344b2fce7.png",
								"key": "水产"
							}
						]
					},
					{
						"name": "粮油副食",
						"foods": [{
								"cat": 393,
								"name": "米面粮油",
								"icon": "http://nq348.com/uploads/category/20220418/1bb32e319ecf5aa352b7fe26fc265004.png",
								"key": "米面粮油"
							},
							{
								"cat": 394,
								"name": "坚果干果",
								"icon": "http://nq348.com/uploads/category/20220418/6ded13eae4a3b113b5225ca8b99bbfdd.png",
								"key": "坚果干果"
							},
							{
								"cat": 395,
								"name": "加工食品",
								"icon": "http://nq348.com/uploads/category/20220418/1e1c10838799de5834aa77f0f9eb8f40.png",
								"key": "加工食品"
							},
							{
								"cat": 396,
								"name": "茶烟酒",
								"icon": "http://nq348.com/uploads/category/20220418/c43cd994e49023c7efdf2b18b1bca30b.png",
								"key": "茶烟酒"
							}
						]
					},
					{
						"name": "花卉苗木",
						"foods": [{
								"cat": 398,
								"name": "鲜花盆景",
								"icon": "http://nq348.com/uploads/category/20220418/b21c44045daaa8b8d148981ba9efc2e0.png",
								"key": "鲜花盆景"
							},
							{
								"cat": 399,
								"name": "果树苗",
								"icon": "http://nq348.com/uploads/category/20220418/63ee2b902ff0f4d638d8a5ad770f7641.png",
								"key": "果树苗"
							},
							{
								"cat": 400,
								"name": "蔬瓜种子",
								"icon": "http://nq348.com/uploads/category/20220418/2df521877616ee44fd01aae0434a5815.png",
								"key": "蔬瓜种子"
							},
							{
								"cat": 401,
								"name": "经济作物",
								"icon": "http://nq348.com/uploads/category/20220418/f85be72a98694befd889f30de45a1d64.png",
								"key": "经济作物"
							}
						]
					},
					{
						"name": "中草药材",
						"foods": [{
								"cat": 403,
								"name": "全草类",
								"icon": "http://nq348.com/uploads/category/20220418/01812c1a83f5db7eafbf3bdae927f134.png",
								"key": "全草类"
							},
							{
								"cat": 405,
								"name": "根茎皮叶花",
								"icon": "http://nq348.com/uploads/category/20220418/dca8dcc814401474d4f19ae7394cc209.png",
								"key": "根茎皮叶花"
							},
							{
								"cat": 406,
								"name": "滋补品类",
								"icon": "http://nq348.com/uploads/category/20220418/33b965295811fdd6f5e672e9a3ce34a2.png",
								"key": "滋补品类"
							},
							{
								"cat": 404,
								"name": "果实籽仁类",
								"icon": "http://nq348.com/uploads/category/20220418/1dc8c46c66b4625d458a7f45787ecef9.png",
								"key": "果实籽仁类"
							}
						]
					},
					{
						"name": "其他",
						"foods": [{
								"cat": 434,
								"name": "包装",
								"icon": "http://nq348.com/uploads/category/20220418/ebdfd326333344825adbe81dbd89e2c9.png",
								"key": "包装"
							},
							{
								"cat": 435,
								"name": "安全溯源",
								"icon": "http://nq348.com/uploads/category/20220418/03230c63f066f46005abf5f576df0ed1.png",
								"key": "安全溯源"
							},
							{
								"cat": 436,
								"name": "农用百货",
								"icon": "http://nq348.com/uploads/category/20220418/93393f2df3264faba86bb449a0c10a79.png",
								"key": "农用百货"
							},
							{
								"cat": 437,
								"name": "仓储物流",
								"icon": "http://nq348.com/uploads/category/20220418/f553505ebabbcb1bf762b288716cf1e7.png",
								"key": "仓储物流"
							}
						]
					}
				], // 渲染的数据，放在最后供你们测试
				arr: [], // 储存距离顶部高度的数组
				scrollRightTop: 0, // 右边栏目scroll-view的滚动条高度
				timer: null, // 定时器

			}
		},
		onReady() {
			this.getMenuItemTop()
		},
		methods: {
			/**
			 * 获取一个目标元素的高度
			 * @elClass 元素的类名
			 * @dataVal 储存高度的对象
			 */
			getElRect(elClass, dataVal) {
				new Promise((resolve, reject) => {
					const query = uni.createSelectorQuery().in(this);
					query.select('.' + elClass).fields({
						size: true
					}, res => {
						// 如果节点尚未生成，res值为null，循环调用执行
						if (!res) {
							setTimeout(() => {
								this.getElRect(elClass);
							}, 10);
							return;
						}
						this[dataVal] = res.height;
						resolve();
					}).exec();
				})
			},
			/**
			 * 获取右边菜单每个item到顶部的距离
			 * 储存到 arr 数组里面用于后面滚动判断
			 */
			getMenuItemTop() {
				new Promise(resolve => {
					let selectorQuery = uni.createSelectorQuery();
					selectorQuery.selectAll('.class-item').boundingClientRect((rects) => {
						// 如果节点尚未生成，rects值为[](因为用selectAll，所以返回的是数组)，循环调用执行
						if (!rects.length) {
							setTimeout(() => {
								this.getMenuItemTop();
							}, 10);
							return;
						}
						rects.forEach((rect) => {
							// 视情况而定，这里减去rects[0].top，是因为第一项顶部可能不是贴到导航栏(比如有个搜索框的情况)
							// this.arr.push(rect.top - rects[0].top);
							this.arr.push(rect.top)
							resolve();
						})
					}).exec()
				})
			},
			/**
			 * 观测元素相交状态
			 * 检测右边scroll-view的id为itemxx的元素与right-box的相交状态
			 * 如果跟.right-box底部相交，就动态设置左边栏目的活动状态
			 */
			async observer() {
				this.tabbar.map((val, index) => {
					let observer = uni.createIntersectionObserver(this);
					observer.relativeTo('.right-box', {
						top: 0
					}).observe('#item' + index, res => {
						if (res.intersectionRatio > 0) {
							let id = res.id.substring(4);
							this.leftMenuStatus(id);
						}
					})
				})
			},
			/**
			 * 设置左边菜单的滚动状态
			 * @index 传入的 ID
			 */
			async leftMenuStatus(index) {
				this.current = index;
				// 如果为0，意味着尚未初始化
				if (this.menuHeight == 0 || this.menuItemHeight == 0) {
					await this.getElRect('menu-scroll-view', 'menuHeight');
					await this.getElRect('u-tab-item', 'menuItemHeight');
				}
				// 将菜单活动item垂直居中
				this.scrollTop = index * this.menuItemHeight + this.menuItemHeight / 2 - this.menuHeight / 2;
			},
			/**
			 * 点击左边的栏目切换
			 * @index 传入的 ID
			 */
			async swichMenu(index) {
				if (this.arr.length == 0) {
					await this.getMenuItemTop();
				}
				if (index == this.current) return;
				this.scrollRightTop = this.oldScrollTop;
				this.$nextTick(function() {
					this.scrollRightTop = this.arr[index];
					this.current = index;
					this.leftMenuStatus(index);
				})
			},
			/**
			 * 右边菜单滚动
			 * 如果不存在height2，意味着数据循环已经到了最后一个，设置左边菜单为最后一项即可
			 */
			async rightScroll(e) {
				this.oldScrollTop = e.detail.scrollTop;
				if (this.arr.length == 0) {
					await this.getMenuItemTop();
				}
				if (this.timer) return;
				if (!this.menuHeight) {
					await this.getElRect('menu-scroll-view', 'menuHeight');
				}
				setTimeout(() => { // 节流
					this.timer = null;
					// scrollHeight为右边菜单垂直中点位置
					// let scrollHeight = e.detail.scrollTop + this.menuHeight / 2;
					// scrollHeight为右边菜单头部位置
					let scrollHeight = e.detail.scrollTop + 20;
					for (let i = 0; i < this.arr.length; i++) {
						let height1 = this.arr[i];
						let height2 = this.arr[i + 1];
						if (!height2 || scrollHeight >= height1 && scrollHeight < height2) {
							this.leftMenuStatus(i);
							return;
						}
					}
				}, 10)
			}
		}


	}
</script>

<style>
	.u-wrap {
		/* #ifdef H5 */
		height: calc(100vh - var(--window-top));
		/* #endif */
		display: flex;
		flex-direction: column;
		height: 100vh;
	}

	.u-search-box {
		padding: 18rpx 30rpx;
	}

	.u-menu-wrap {
		flex: 1;
		display: flex;
		overflow: hidden;
	}

	.u-tab-view {
		width: 200rpx;
		height: 100%;
	}

	.u-tab-item {
		height: 110rpx;
		background: #f6f6f6;
		box-sizing: border-box;
		display: flex;
		align-items: center;
		justify-content: center;
		font-size: 26rpx;
		color: #444;
		font-weight: 400;
		line-height: 1;
	}

	.u-tab-item-active {
		position: relative;
		color: #06A446;
		font-size: 30rpx;
		font-weight: 500;
		background: #D6FFE7;
	}

	.u-tab-item-active::before {
		content: "";
		position: absolute;
		border-left: 4px solid #06A446;
		height: 52rpx;
		left: 0;
		top: 29rpx;
	}

	.u-tab-view {
		height: 100%;
	}

	.right-box {
		background-color: rgb(250, 250, 250);
	}

	.page-view {
		padding: 16rpx;
	}

	.class-item {
		margin-bottom: 30rpx;
		background-color: #fff;
		padding: 16rpx;
		border-radius: 8rpx;
	}

	.class-item:last-child {
		min-height: 100vh;
	}

	.item-title {
		font-size: 26rpx;
		color: $u-main-color;
		font-weight: bold;
	}

	.item-menu-name {
		margin-top: 8rpx;
		font-weight: normal;
		font-size: 24rpx;
		color: $u-main-color;
	}

	.item-container {
		display: flex;
		flex-wrap: wrap;
	}

	.thumb-box {
		width: 33.333333%;
		display: flex;
		align-items: center;
		justify-content: center;
		flex-direction: column;
		margin-top: 20rpx;
	}

	.item-menu-image {
		width: 120rpx;
		height: 120rpx;
	}
</style>
